The immune system of higher animals comprised of two parts: Innate – or Natural – (INIM-NIM) and Adaptive Immunity (ADIM). Innate resistance includes physical barriers (e.g. skin, cornea, mucous membranes, the blood-brain barrier - BBB) chemical defense (HCl in the stomach, bile acids in the intestines, enzyme based protection) and Species Specific Resistance (SSR) to viruses and other pathogens. SSR may occur because of the lack of proper receptors for the pathogen to establish itself in the resistant animal species. Therefore, SSR is a phylogenetically determined property of various animal species. Innate immunity includes polyspecifc immune mechanisms with germ line gene based antigen receptors (INIR/NIR) that recognize phylogenetically preserved, highly cross-reactive (homologous) epitopes, or homotopes. Because both the antigen receptors (e.g. toll-like receptors - TLR) and the homotopes (e.g., lipid A in bacterial lipopolysaccharide - LPS) are constant, and fully differentiated immune (monocyte/macrophages and other leucocytes) and somatic cells express TLR, the entire organism is capable of responding instantaneously to infection or injury. Innate phagocytes, primarily monocyte/macrophages, support the development of adaptive immunity, by presenting antigen and by contributing cytokines for cell activation. If natural immunity is depressed, ADIM will be deficient. The natural immune system provides continuous protection for the host animals or men against the effects of stress, treatment of cytostatic drugs, septic shock, infectious diseases, and numerous other noxious agents. Neuroendocrine, nutritional and environmental factors regulate natural immunity. The maintenance of good NIM defense is most important in modern medicine. Radiodetoxified endotoxin (RD-LPS) stimulates NIM, and activates the bone marrow. Animal experiments and human studies showed that RD-LPS is a promising preparation for the elevation of natural immunity. RD-LPS is a potent immunological adjuvant in the case of inactivated virus vaccines (e.g. influenza).